U.S. Army Sergeant Bowe Bergdahl endured some of the worst abuse any U.S. prisoner of war has seen for decades while being held for five years by the Taliban in Afghanistan, a defense official has testified.

Bergdahl suffered torture, abuse, and neglect, including months of beatings, said Terrence Russell, an expert with the military's Joint Personnel Recovery Agency.

He was held for 3 1/2 years in a metal cage barely big enough to stand, living in isolation, and often blindfolded, Russell told a U.S Army hearing in Texas on September 18. Any more beatings would have killed him, Russell said.

"His experience ranks at the same echelon of the most horrible conditions of the last 60 years," said Russell, who debriefed Bergdahl after he was swapped last year for five Taliban leaders held by the United States in a controversial prisoner exchange.

Bergdahl, 29, who is charged with desertion, never gave up trying to escape, Russell said, dismissing as outrageous claims that Bergdahl was a Taliban sympathizer.

"He had to fight the enemy alone for four years and 11 months," Russell said, occasionally wiping back tears.